The invention relates to a method for the time-dependent, automatic measurement of the backscattered portions of light pulses coupled into an optical fibre under test, said portions being received by an optical detector and converted into electrical measurement signals, followed by amplification by a gain factor adapted to the measurement range, application to an electronic evaluation circuit and storage in a memory wherefrom they can be fetched for display on a display device.
A method of this kind is known from IEEE Journal of Quantum Electronics, Vol. QE-17, Pages 1264 to 1269. Therein, selected time domains of the optical backscattered signals are examined using an adapted gain factor, so that either the available dynamic range of an amplifier can be fully utilized or, in the case of a given dynamic range, a longer measurement length of an optical fibre can be examined. However, the known method is only capable of covering a part of the length of an optical fibre in the case of an automatic measurement. The dynamic range expansion will not be obtained when the entire length of a long optical fibre is to be measured in a single operation and the variation of the attenuation values as a function of location along the entire length of the optical fibre is to be subsequently represented as a single, continuous curve.